It looks like marketers are in the process of demanding more granular measurement than the aggregate C3 ratings for a show, instead they want measurement of each commercial. From Advertising Age:

NEW YORK (AdAge.com) -- When marketers, ad buyers, TV networks and Nielsen lurched toward a mid-2007 agreement that allowed payment for TV ads to be based on the number of people who watched them -- not on the viewership of the shows they interrupted -- it was seen as a landmark. Less than two years later, marketers are already pressing for an even-more granular measurement: how many watched their ads.

Current commercial ratings -- known as C3 because they measure three days' worth of viewing -- hinge on figuring out how many viewers didn't skip past an "average commercial minute" in a particular program. Marketers would rather payment be based on the viewership of each commercial. The amount Nike paid would depend on the number of people who watched its latest iteration of "Just Do It," while the amount of cash McDonald's would fork over would be based on how many actually saw one of its Burgers in a TV spot in real time.

What's wrong with the current data? At a time when the web is revealing so much specific information about the relationship of consumers and their reactions to ads, marketers feel TV ought to do the same.

So what's the rub? It seems the rub is that marketers want this data, but aren't necessarily willing to pay for it!

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In other words, Nielsen has been down this road before. Tight-fisted advertisers trying to muddle though a difficult economy have already pulled back on media spending, so how willing will they be this year to spend money on the research that helps justify that spending? Marketers pay a lot of lip service to the ideal of linking every dollar they spend to sales boosts, lead generation and market-share increases. But many of Nielsen's recent efforts to create a market in this area have floundered. - read the full story on Adage.com